The
exec family of functions replaces the current process image with a new process
image. The functions described in this manual page are front-ends for the
function
execve(2) . (See the manual page for
execve for detailed information about the replacement of the current process.)
The initial argument for these functions is the pathname of a file which is
to be executed.
The
"const char *arg" and subsequent ellipses in the
execl , execlp , and
execle functions can be thought of as
arg0 , arg1 , ...,
argn . Together they describe a list of one or more pointers to null-terminated
strings that represent the argument list available to the executed program.
The first argument, by convention, should point to the file name associated
with the file being executed. The list of arguments
must be terminated by a
NULL pointer.
The
execv and
execvp functions provide an array of pointers to null-terminated strings that
represent the argument list available to the new program. The first
argument, by convention, should point to the file name associated with the
file being executed. The array of pointers
must be terminated by a
NULL pointer.
The
execle function also specifies the environment of the executed process by following
the
NULL pointer that terminates the list of arguments in the parameter list or the
pointer to the argv array with an additional parameter. This additional
parameter is an array of pointers to null-terminated strings and
must be terminated by a
NULL pointer. The other functions take the environment for the new process
image from the external variable
environ in the current process.
Some of these functions have special semantics.
The functions
execlp and
execvp will duplicate the actions of the shell in searching for an executable file
if the specified file name does not contain a slash (/) character. The
search path is the path specified in the environment by the
PATH variable. If this variable isn't specified, the default path
``:/bin:/usr/bin'' is used. In addition, certain
errors are treated specially.
If permission is denied for a file (the attempted
execve returned
EACCES ), these functions will continue searching the rest of the search path. If no
other file is found, however, they will return with the global variable
errno set to
EACCES .
If the header of a file isn't recognized (the attempted
execve returned
ENOEXEC ), these functions will execute the shell with the path of the file as its
first argument. (If this attempt fails, no further searching is done.)
RETURN VALUE
If any of the
exec functions returns, an error will have occurred. The return value is -1,
and the global variable
errno will be set to indicate the error.
FILES
/bin/sh
ERRORS
All of these functions may fail and set
errno for any of the errors specified for the library function
execve(2) .
On some other systems the default path (used when the environment
does not contain the variable PATH) has the current working
directory listed after
/binand
/usr/bin , as an anti-Trojan-horse measure. Linux uses here the
traditional "current directory first" default path.
The behavior of
execlp and
execvp when errors occur while attempting to execute the file is historic
practice, but has not traditionally been documented and is not specified by
the POSIX standard. BSD (and possibly other systems) do an automatic
sleep and retry if ETXTBSY is encountered. Linux treats it as a hard
error and returns immediately.
Traditionally, the functions
execlp and
execvp ignored all errors except for the ones described above and
ENOMEM and
E2BIG , upon which they returned. They now return if any error other than the ones
described above occurs.
CONFORMING TO
execl , execv , execle , execlp and
execvp conform to
IEEE Std1003.1-88 (``POSIX.1'').
